CP Chemistry Molar Volume of a Gas Lab PURPOSE: Use the ideal gas law to calculate the actual yield in moles of a gas in a chemical reaction and the percent yield from the theoretical yield. MATERIALS: gas collecting tube thermometer magnesium ribbon 1-hole stopper 10mL syringe 6M HCl 100mL beaker copper wire 1L cylinder metric ruler PROCEDURE: 1. Fill a 100mL beaker with tap water and allow to come to room temperature. 2. From your teacher obtain and record both current room temperature (°C) and atmospheric pressure (mmHg). 3. Obtain a piece of magnesium ribbon from your teacher and measure and record its length to the nearest .1 cm. Record the mass (provided by the teacher) of one meter of magnesium ribbon. 4. Carefully fold the magnesium ribbon into a ball small enough to fit into the mouth of the gas collecting tube. Use the copper wire to enclose the magnesium in a small cage, leaving 3-4 cm of wire. 5. Measure and record the temperature of the tap water in the 100mL beaker. 6. Fill a 1L cylinder to within 2 or 3 centimeters of the top. 7. Use the syringe to place 10 mL of 6M HCl into the gas collecting tube. While holding the gas collecting tube at a 45° angle, delicately pour the room temperature tap water into the gas collecting tube so that it lithely slides down the side of the tube and comes to rest on top of the HCl, without mixing with the HCL. (Since the density of the acid is greater than that of the water, the water will tend to float on top of the acid for a brief period of time.) Fill the tube all the way to the top. 8. With the tube completely full of water, insert the ball of Mg ribbon attached to the copper wire about 3 or 4 cm into the tube. While holding the magnesium on the wire against the side of the tube, insert the stopper so that it forces all of the excess water and air bubbles out of the tube. Let the excess water & air squeeze out of the hole in the rubber stopper as you insert it. 9. With your finger over the hole in the stopper and another person securely holding the cylinder, invert the gas collecting tube and place the stoppered end into the cylinder of water. 10. Once the stopper is under the water, remove your finger and hold the tubein the water throughout the reaction. The reaction will begin when the heavier acid diffuses to the bottom of the tube and contacts the Mg ribbon. 11. When the reaction is completed (no more bubbling), tap the side of the gas collecting tube so that all of the bubbles rise to the top. 12. Position the gas collecting tube so that its water level exactly matches the water level of the cylinder. When both levels match, the pressure of the gas in the gas collecting is equal to atmospheric pressure. While holding the tube in this position, read and record the exact volume of the hydrogen gas. 13. Rinse the gas tube cylinder and beaker thoroughly. CALCULATIONS:(Show the following calculations) 1. Write the balanced equation for the reaction of Mg with HCL to produce hydrogen gas. 2. Calculate the mass of magnesium used. 3. Using your balanced equation and the calculated mass of the magnesium, calculate and record the theoretical yield of hydrogen gas in moles. 4. Using the ideal gas law calculate and record the actual number of moles of hydrogen gas that were produced. 5. Using the theoretical yield and the actual yield, calculate and record the % yield.
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